The secretory process in several cell types is being investigated. The rat basophilic leukemia cell line (RBL-2H3) and other cultured cells are used to study various aspects of endocytic and secretory processes. Emphasis is on the use of morphological, cytochemical and biochemical characterizations in these cultured cells. Events involved in receptor activation and signal transduction are being investigated, as well as endocytic and secretory pathways. During the last year emphasis has been on the study of the biochemical changes induced by the binding of a monoclonal antibody to a cell surface ganglioside.